CN112088073B

CN112088073B - Articulated robot and method for estimating gas reduction state of gas spring thereof

Info

Publication number: CN112088073B
Application number: CN201980030911.XA
Authority: CN
Inventors: 藤井勇辅
Original assignee: Kawasaki Jukogyo KK
Current assignee: Kawasaki Motors Ltd
Priority date: 2018-05-10
Filing date: 2019-05-09
Publication date: 2023-08-01
Anticipated expiration: 2039-05-09
Also published as: EP3792014B1; JP7084202B2; TWI701119B; US20210069919A1; US11376731B2; WO2019216382A1; TW201946746A; JP2019195880A; EP3792014A4; CN112088073A; EP3792014A1

Abstract

A robot (2) is provided with an arm support (12), a rotating arm (14) rotatably supported by the arm support (12), a drive motor for rotating the rotating arm (14), a gas spring (8) for supporting a load acting on the rotating arm (14) and reducing the load of the drive motor, and a control device (10). The control device (10) has the following functions: judging the condition that the rotating arm (14) is in a rotating state; a reduced state of the gas spring (8) is estimated based on a comparison between an actual current value and a theoretical current value of the drive motor when the rotating arm (14) is in a rotating state.

Description

Articulated robot and method for estimating gas reduction state of gas spring thereof

Technical Field

The present invention relates to an articulated robot and a method for estimating a gas reduction state of a gas spring thereof.

Background

An articulated robot is disclosed in Japanese patent application laid-open No. 2017-159402. The robot includes an arm, a drive motor for rotating the arm, and a gas spring. The gas spring supports a load acting on the arm, and reduces the load of the drive motor.

The gas spring generates a balance force for reducing the load of the drive motor by the pressure (hereinafter, also referred to as gas pressure) of the enclosed gas. The gas enclosed in the gas spring leaks due to long-term use. This leakage of gas reduces the gas pressure. This decrease in air pressure decreases the balance force generated by the gas spring. This decrease in the balance force increases the load on the drive motor.

The control mechanism of the robot has a function of estimating the gas reduction state of the gas spring. The control means acquires an actual current value of the drive motor in a state in which the drive motor is driven and the arm is stopped. The control means estimates a decrease state of the gas based on the actual current value. When the gas reduction state is a predetermined reduction state, the control means notifies the gas reduction state. In this way, in the robot, the load of the drive motor is prevented from becoming excessive due to leakage of gas.

Patent document 1: japanese patent laid-open publication No. 2017-1594402

As described above, in this robot, the actual current value of the drive motor is obtained in a state in which the drive motor is driven and the arm is stopped. In the stopped state of the arm, a static frictional force acts on the arm. The arm stops before the magnitude of the static friction exceeds the maximum static friction. In the stopped state of the arm, the actually applied static friction force varies. The deviation of the static friction force causes a deviation of torque of the drive motor in a stopped state of the arm. The deviation of the torque of the drive motor also causes a deviation of the actual current value of the drive motor. This deviation in the actual current value reduces the accuracy of estimating the reduced state of the gas.

Disclosure of Invention

The purpose of the present invention is to provide a robot capable of accurately estimating the gas reduction state of a gas spring, and a method for estimating the gas reduction state of the gas spring using the robot.

The articulated robot according to the present invention includes: an arm support part; a rotating arm rotatably supported by the arm support part; a driving motor for rotating the rotating arm; a gas spring for supporting a load acting on the rotating arm to reduce the load of the driving motor; and a control device.

The control device has the following functions: judging the condition that the rotating arm is in a rotating state; the gas spring is configured to be rotated by the rotating arm, and the gas spring is configured to be rotated by the rotating arm.

Another articulated robot according to the present invention includes: an arm support part; a rotating arm rotatably supported by the arm support part; a driving motor for rotating the rotating arm; a gas spring for supporting a load acting on the rotating arm to reduce the load of the driving motor; and a control device. The control device has the following functions: the gas spring is configured to be rotated by the rotating arm, and the gas spring is configured to be rotated by the rotating arm.

Preferably, the control device has the following functions: the magnitude of the fluctuation of the angular acceleration of the drive motor is determined.

Preferably, the control device uses an actual current value when the rotating arm is in a posture that generates a torque of 25% or more of a maximum torque borne by the gas spring.

In the gas reduction amount estimation method according to the present invention, in a joint robot including a rotating arm, a driving motor that rotates the rotating arm, and a gas spring that supports a load acting on the rotating arm and reduces the load of the driving motor, a gas reduction state of the gas spring is estimated. The method comprises the following steps: an actual current value obtaining step of obtaining an actual current value of the drive motor; and estimating a gas reduction state of the gas spring based on the actual current value. In the actual current value obtaining step, the actual current value when the rotating arm is in a rotating state is obtained. In the estimating step, a gas reduction state of the gas spring is estimated based on a comparison between the actual current value and the theoretical current value obtained in the actual current value obtaining step.

The robot according to the present invention estimates the gas reduction state of the gas spring based on the actual current value of the rotating arm in the rotating state. In a state where the static friction force has not acted on the rotating arm, the robot estimates a state of reduction of the gas spring. In this robot, the state of reduction of the gas spring can be estimated with high accuracy. In the gas reduction state estimation method using the robot, the reduction state of the gas can be estimated with high accuracy.

Drawings

Fig. 1 is a side view showing an articulated robot according to an embodiment of the present invention.

Fig. 2 (a) is an explanatory view showing a state of use of the gas spring of the robot of fig. 1, and fig. 2 (b) is an explanatory view showing another state of use of the gas spring.

Fig. 3 is an explanatory view of a use state of a gas spring of the robot of fig. 1.

Fig. 4 (a) is an explanatory diagram of a relation between the torque of the gas spring and the torque of the drive motor in the initial set state of the robot of fig. 1, and fig. 4 (b) is an explanatory diagram of a relation between the torque of the gas spring and the torque of the drive motor in the reduced state of the gas.

Fig. 5 is an explanatory diagram showing a change in the pressure Pa of the gas spring during the operation of the robot in fig. 1.

Fig. 6 (a) is a graph showing the air pressure obtained by the estimation method according to the present invention using the robot of fig. 1 at the air pressure P1 and the air pressure obtained by the conventional estimation method, fig. 6 (b) is a graph showing the air pressure obtained by the estimation method according to the present invention at another air pressure P2 and the air pressure obtained by the conventional estimation method, and fig. 6 (c) is a graph showing the air pressure obtained by the estimation method according to the present invention and the air pressure obtained by the conventional estimation method at another air pressure P3.

Fig. 7 (a) is a graph showing the distribution of air pressure obtained by the estimation method according to the present invention using the robot of fig. 1, and fig. 7 (b) is a graph showing the distribution of air pressure obtained by another estimation method according to the present invention.

Fig. 8 is a graph showing a relationship between the air pressure obtained by the estimation method according to the present invention using the robot of fig. 1 and the angle θc of the second arm.

Detailed Description

The present invention will be described in detail below based on preferred embodiments with appropriate reference to the accompanying drawings.

Fig. 1 shows a robot 2 according to the present invention. The robot 2 includes a base 4, a robot arm 6, a gas spring 8, and a control device 10. Although not shown, the robot 2 further includes driving motors M1 to M6, rotation sensors E1 to E6, and current sensors C1 to C6.

The robot arm 6 includes a first arm 12, a second arm 14, a third arm 16, a fourth arm 18, a fifth arm 20, and a sixth arm 22. In the robot 2, the base 4, the first arm 12, the second arm 14, the third arm 16, the fourth arm 18, the fifth arm 20, and the sixth arm 22 are connected in this order. The robot 2 includes a plurality of joints as the connecting portions. The robot 2 is a so-called articulated robot.

As shown in fig. 1, in this robot 2, a hand 24 is attached to the tip of the sixth arm 22. The hand 24 has a function of gripping a workpiece, not shown. The hand 24 is an example of a tool attached to the robot 2, and other tools may be attached.

In the robot 2, the first arm 12 is coupled to the base 4 so as to be rotatable about the vertical axis L1 as a rotation axis. The second arm 14 is rotatably coupled to the first arm 12 with the axis L2 in the horizontal direction as a rotation axis. The third arm 16 is rotatably coupled to the second arm 14 about a horizontal axis L3. The fourth arm 18 is rotatably coupled to the third arm 16 with the axis L4 thereof as a rotation axis. The fifth arm 20 is rotatably coupled to the fourth arm 18 with an axis L5 orthogonal to the axis L4 as a rotation axis. The sixth arm 22 is rotatably coupled to the fifth arm 20 with the axis L6 thereof as a rotation axis. Here, the present invention will be described with the second arm 14 as a rotating arm and the first arm 12 as an arm support.

The drive motor M1 has a function of rotating the first arm 12. The drive motor M1 is controlled by the control device 10. The driving motor M1 is, for example, a servo motor. The drive motor M2 has a function of rotating the second arm 14. The drive motor M2 is controlled by the control device 10. The driving motor M2 is, for example, a servo motor. Similarly, the drive motors M3 and M5 have a function of rotating the third arm 16 and the fifth arm 20, and the drive motors M4 and M6 have a function of rotating the fourth arm 18 and the sixth arm 22. The drive motors M3, M4, M5, and M6 are controlled by the control device 10. The driving motors M3, M4, M5, and M6 are servo motors, for example.

The rotation sensor E1 has a function of detecting the rotation position of the drive motor M1. The rotation sensor E2 has a function of detecting the rotation position of the drive motor M2. Similarly, the rotation sensors E3, E4, E5, and E6 have a function of detecting the rotation positions of the drive motors M3, M4, M5, and M6. The rotation sensors E1, E2, E3, E4, E5, and E6 are, for example, encoders.

The current sensor C1 has a function of detecting a current for controlling the rotation of the drive motor M1. The current sensor C2 has a function of detecting a current for controlling the rotation of the drive motor M2. Similarly, the current sensors C3, C4, C5, and C6 have a function of detecting a current for controlling the rotation of the drive motors M3, M4, M5, and M6.

The gas spring 8 is pivotally connected at its base end portion 8b to a first arm 12 serving as an arm support portion. The gas spring 8 is pivotally connected at its distal end portion 8c to a second arm 14 as a pivoting arm. The gas spring 8 is capable of expanding and contracting between the base end portion 8b and the tip end portion 8c. The gas spring 8 can rotate in association with the rotation of the second arm 14.

Reference numeral Pa in fig. 1 denotes the rotation center of the second arm 14. Reference numeral Pb denotes a rotation center of the base end portion 8b of the gas spring 8. Reference numeral Pc denotes a rotation center of the front end portion 8c of the gas spring 8. The double-headed arrow S indicates the distance from the rotation center Pb of the base end portion 8b to the rotation center Pc of the tip end portion 8c. The distance S varies according to the expansion and contraction of the gas spring 8.

The control device 10 includes an input/output unit for inputting/outputting data, a storage unit for storing data, and an arithmetic unit for calculating data. The control device 10 has a function of controlling the rotation of each of the drive motors M1 to M6. The control device 10 has a function of receiving rotational position information of the drive motors M1 to M6 from the respective rotation sensors E1 to E6. The control device 10 has a function of specifying the rotational positions of the first arm 12, the fourth arm 18, and the sixth arm 22 and the rotational positions of the second arm 14, the third arm 16, and the fifth arm 20. The control device 10 has a function of receiving the current values of the current sensors C1 to C6. The control device 10 has a function of calculating the torque of the drive motors M1 to M6 from the current values of the drive motors M1 to M6.

Fig. 2 (a) shows a state of use of the gas spring 8 shown in fig. 1. The gas spring 8 includes a cylinder 26 and a piston 28. The cylinder 26 is mounted to the base end portion 8b. The piston 28 is mounted to the front end portion 8c. The piston 28 is slidably inserted into the cylinder 26. The piston 28 and cylinder 26 form a gas chamber 30. The gas chamber 30 is filled with a high-pressure gas. The gas is not particularly limited, but is, for example, an inert gas.

Fig. 2 (b) shows a use state in which the entire length of the gas spring 8 in fig. 2 (a) is extended. The distance S of fig. 2 (b) is greater than the distance S of fig. 2 (a). In fig. 2 (b), the gas chamber 30 is reduced in volume by extending the entire length of the gas spring 8. In the use state of fig. 2 (b), the gas of the gas chamber 30 is compressed as compared with the use state of fig. 2 (a). In the gas spring 8 of fig. 2 (b), a larger force acts in the direction in which the total length of the gas spring 8 is shortened than in fig. 2 (a).

In addition, when the gas spring 8 extends over its entire length, a force in the direction in which the entire length thereof is shortened acts. The base end 8b of the gas spring 8 may be pivoted to the second arm 14 instead of the first arm 12, and the tip end 8c may be pivoted to the first arm 12 instead of the second arm 14. The gas spring 8 may serve to support the load acting on the second arm 14 and reduce the load of the drive motor M2. The gas spring 8 may be configured to exert a force in a direction in which the entire length thereof extends when the entire length thereof is shortened. When the total length of the gas spring 8 is shortened, the force in the direction in which the total length extends may be applied, so that the load on the drive motor M2 may be reduced.

Fig. 3 shows the positional relationship among rotation centers Pa, pb, and Pc of the robot 2 of fig. 1. In fig. 3, the positional relationship of these is shown by projection onto a plane parallel to the paper surface of fig. 1. The chain line C indicates the locus of the rotation center Pc that moves with the rotation of the second arm 14 of fig. 1. The locus C is an arc centered on the rotation center Pa. The two-dot chain line Lb indicates a reference line. The reference line Lb is a straight line extending through the rotation center Pa and the rotation center Pb.

Reference numeral Pc1 denotes an intersection point of the locus C and the reference line Lb. The two-dot chain line C' indicates a trajectory of an arc inscribed on the trajectory C at the intersection Pc1 with the rotation center Pb as the center. The double arrow S1 indicates the distance from the rotation center Pb to the intersection point Pc 1. In fig. 3, this distance S1 is obtained as a linear distance between the rotation center Pb and the intersection point Pc 1. The distance S1 is the radius of the track C'.

The two-dot chain line Lc represents an imaginary line. The virtual line Lc is a straight line extending in the radial direction of the track C through the rotation center Pa. Reference numeral Pc2 denotes an intersection point of the locus C and the virtual line Lc. The two-dot chain line Ld is a straight line extending through the rotation center Pb and the intersection point Pc 2. Reference numeral Pc 'denotes an intersection of the straight line Ld and the locus C'. The double arrow S2 indicates the distance from the rotation center Pb to the intersection point Pc 2. In fig. 3, this distance S2 is obtained as a linear distance between the rotation center Pb and the intersection point Pc 2. The double-headed arrow θc indicates an angle formed between the reference line Lb and the virtual line Lc. This angle θc is shown in fig. 3 as 0 ° with reference line Lb, positive clockwise, and negative counterclockwise.

In the robot 2, when the second arm 14 rotates and the rotation center Pc in fig. 1 moves to the intersection point Pc1, the distance S of the gas spring 8 is set to be the distance S1. The distance S1 is the minimum value of the distance S. When the second arm 14 rotates and the rotation center Pc moves to the intersection point Pc2, the distance S is set to be the distance S2. At this time, the distance S of the gas spring 8 extends from the distance S1 to the distance S2. The gas spring 8 expands by a difference between the distance S1 and the distance S2 (S2-S1).

That is, the rotation center Pc moves from the intersection point Pc1 to the intersection point Pc2, and the distance S of the gas spring 8 is elongated by a difference (S2-S1). At this time, the gas is compressed, and the gas spring 8 generates a force in a direction in which the entire length thereof is shortened. This gas spring 8 thus functions to support the load acting on the rotating second arm 14 and to reduce the load of the drive motor M2.

Fig. 4 (a) schematically shows the torque Tm generated by the drive motor M2 and the torque Tg generated by the gas spring 8. Fig. 4 (a) shows the torque Tm and the torque Tg of the robot 2 in a certain posture in which the second arm 14 is in a rotated state. Fig. 4 (a) shows the torque Tm and the torque Tg in the initial set state in which no gas leaks. The second arm 14 in the rotated state performs a predetermined rotational operation by applying the torque Tg and the torque Tm.

Fig. 4 (b) shows the torque Tm and the torque Tg in a state where a part of the gas leaks. Fig. 4 (b) shows the torque Tm and the torque Tg of the robot 2 in the same posture as fig. 4 (a). In fig. 4 (b), the torque Tg borne by the gas spring 8 is reduced due to the leakage of the gas. The torque Tg decreases by a decrease amount Δt. In order to perform a predetermined turning operation of the second arm 14, the torque Tm generated by the drive motor M2 increases. The torque Tm increases by a decrease amount Δt.

In the robot 2, an angle θc is determined based on the posture of the second arm 14 (see fig. 3). The distance S of the gas spring 8 is also uniquely determined. Therefore, in the initial set state in which the gas does not leak, the torque Tg of the gas spring 8 is also determined according to the posture of the second arm 14. Based on the torque Tg determined by the posture of the second arm 14, the torque Tm to be borne by the drive motor M2 is also uniquely determined. If the torque Tm is determined, a current value to be supplied to the drive motor M2 can be calculated based on the current-torque characteristic of the drive motor M2.

As shown in fig. 4 (b), if a part of the gas spring 8 leaks and the gas pressure decreases, the torque Tg of the gas spring 8 decreases. In order to cause the second arm 14 to perform a predetermined operation, the torque Tm of the drive motor M2 is increased to compensate for the decrease Δt in the torque Tg. The increased torque Tm can be calculated from the actual current value of the drive motor M2 based on the current-torque characteristic of the drive motor M2.

Here, a gas reduction state estimation method according to the present invention will be described with reference to the robot 2. The gas reduction state estimation method is a method of estimating the reduction amount of the gas spring 8 at any time after the start of the use of the gas spring 8 of the robot 2.

The gas reduction state estimation method includes a preparation STEP (STEP 1), an actual current value acquisition STEP (STEP 2), and an estimation STEP (STEP 3).

In the preparation STEP (STEP 1), the control device 10 stores the coefficient K obtained in advance. The coefficient K is obtained from the actual current value Im and a theoretical current value Ii described later. The actual current value Im is acquired as an actual current value from the driving motor M2 that is driven. The theoretical current value Ii is obtained as a calculated current value of the drive motor M2. The coefficient K is calculated as a ratio (Ii/Im) of the theoretical current value Ii to the actual current value Im.

The theoretical current value Ii is a current value to be supplied to the drive motor M2 in a set state in the initial air pressure Pi of the air spring 8. In this set state, the torque Tm to be applied to the drive motor M2 is uniquely determined according to the rotational posture of the second arm 14. Based on the current-torque characteristic of the drive motor M2, the theoretical current value Ii is obtained from the torque Tm to be applied to the drive motor M2. In order to detect a collision, conventionally, a theoretical current value Ii taking into consideration kinetic friction force is obtained, and the control device 10 stores the theoretical current value Ii.

For example, the control device 10 acquires the actual current value Im of the drive motor M2 from the current sensor C2 in a plurality of postures in which the second arm 14 is in different rotation states. The control device 10 obtains and stores the theoretical current value Ii of the drive motor M2 corresponding to each posture. The control device 10 obtains a ratio (Ii/Im) from the theoretical current value Ii and the actual current value Im. The control device 10 obtains the coefficient K as an average value of these ratios (Ii/Im). If the deviation of the coefficient K is small, the control device 10 stores the coefficient K.

If the deviation of the coefficient K is large, for example, a region in which the range of the posture of the second arm 14 in the rotation state is divided is set. The coefficient K is obtained for each set region. The region may be divided into a range including the posture of the second arm 14 and a range including the postures of the first arm 12 to the sixth arm 22. In this case, the control device 10 stores the set region and the coefficient K corresponding to the region.

The actual current value acquisition STEP (STEP 2) includes a determination STEP (STEP 2-1) and a rotational actual current value acquisition STEP (STEP 2-2). In the actual current value acquisition STEP (STEP 2), the control device 10 determines whether or not the second arm 14 is in a rotation state. In the actual rotation current value acquisition STEP (STEP 2-2), the control device 10 acquires the actual rotation current value Im of the second arm 14. This actual current value Im is also specifically referred to as a rotation actual current value Ir.

For example, in the actual current value acquisition STEP (STEP 2), the control device 10 acquires the actual current value Im in a series of operations of the robot 2. The actual current value Im is obtained, for example, as an average value of current values of a predetermined time period in which the second arm 14 is in a rotation state. The average value of the current values can be obtained by dividing the integrated amount integrated over a predetermined time by the predetermined time. The predetermined time may be several seconds or several minutes.

The control device 10 stores the actual current value Im (rotational actual current value Ir) when the second arm 14 is in the rotational state instead of the stopped state, based on the actual current value Im corresponding to the series of operations.

The method of acquiring the actual rotation current value Ir is exemplified, but not limited thereto. In this method, the rotation actual current value Ir of the second arm 14, which does not include the actual current value Im during the stop of the second arm 14, may be acquired. For example, the control device 10 may determine whether or not the second arm 14 is in the rotation state before acquiring the actual current value Im. Then, the control device 10 may acquire the actual current value Im when the second arm 14 is in the rotated state.

In the estimating STEP (STEP 3), the control device 10 estimates the state of decrease in the gas of the gas spring 8. The control device 10 estimates the gas reduction state by, for example, obtaining the gas pressure reduction pressure Δp. Specifically, the control device 10 obtains the air pressure decrease pressure Δp from the coefficient K, the rotation actual current value Ir, the theoretical current value Ii, and the virtual current value Ig described later, in the state where the second arm 14 is rotated.

The virtual current value Ig is a current value when the drive motor M2 generates the torque Tg of the gas spring 8. In the initial set state of the gas spring 8 at the gas pressure Pi, the torque Tg to be applied to the gas spring 8 is uniquely determined. In this set state, the torque Tg is determined according to the rotational posture of the second arm 14. Based on the current-torque characteristic of the drive motor M2, the virtual current value Ig when the drive motor M2 generates the torque Tg is obtained.

As shown in fig. 4 (a) and 4 (b), when the air pressure of the air spring 8 is reduced, the torque Tm of the drive motor M2 is increased by a reduction amount Δt in order to cause the second arm 14 to perform a predetermined operation. The driving motor M2 increases the actual current value Im (the rotation actual current value Ir) with an increase in the decrease amount Δt. Therefore, the control device 10 can calculate the rate Gp of decrease in the air pressure of the air spring 8 according to the following expression (1). Further, as the initial air pressure Pi, the control device 10 can calculate the reduced pressure Δp of the air pressure according to the following expression (2).

Gp＝(K·Im－Ii)/Ig (1)

ΔP＝Pi·Gp (2)

The control device 10 stores a threshold Δpr of the reduced pressure Δp. In the estimating STEP (STEP 3), when the reduced pressure Δp is equal to or higher than the threshold Δpr, the robot 2 issues an alarm by an alarm (not shown). Then, when the robot 2 returns to the predetermined stop position, the robot is stopped and put into a standby state.

In the robot 2, the reduction pressure Δp is estimated based on a comparison between the actual current value Im (rotation actual current value Ir) at which the second arm 14 is in the rotation state and the theoretical current value Ii. In the robot 2, the actual current value Im when the second arm 14 is in the stopped state is not used, and the reduction pressure Δp is estimated.

In the stopped state of the second arm 14, a stationary frictional force acts on the second arm 14. Since the static friction force acts, the torque Tm of the drive motor M2 and the actual current value Im deviate in the stopped state of the second arm 14. Due to this deviation, the estimated reduction pressure Δp based on the actual current value Im of the second arm 14 in the stopped state is prone to error. The control device 10 of the robot 2 estimates the reduction pressure Δp based on the actual current value Im (rotation actual current value Ir) of the second arm 14 in the rotation state. The second arm 14 in the rotating state does not exert a static friction force and does exert a certain dynamic friction force. In the second arm 14 in the rotation state in which the kinetic friction force acts, the increase or decrease in the torque Tm of the drive motor M2 increases or decreases the rotation speed of the second arm 14. In the second arm 14 in the rotating state, the increase or decrease in the actual current value Im of the drive motor M2 increases or decreases the rotation speed of the second arm 14. The control device 10 estimates the reduced pressure Δp based on the actual current value Im (the rotation actual current value Ir) in the second arm 14 in the rotation state, and can estimate the reduced pressure Δp with high accuracy. The control device 10 of the robot 2 can accurately estimate the state of reduction of the gas spring 8.

In the robot 2, the reduction pressure Δp can be estimated at any time during operation. In this robot 2, no special operation is required for estimating the reduced state of the gas. The robot 2 can infer the reduced state of the gas without stopping the production line. In addition, the reduced pressure Δp can be estimated immediately while the robot 2 is operated. When the gas reduction state is a predetermined state, an alarm can be immediately given. The robot 2 can avoid malfunction and failure caused by the reduction of the gas spring 8.

When the angular acceleration of the drive motor M2 varies greatly, the actual current value Im measured by the drive motor M2 also varies greatly. The actual current value Im with large variation reduces the estimation accuracy of the reduced pressure Δp. From the viewpoint of improving the estimation accuracy, it is preferable that the angular acceleration change rate per unit time of the drive motor M2, that is, the angular acceleration change is small. From this point of view, the control device 10 preferably has a function of determining the magnitude of the fluctuation of the angular acceleration. The preferred control device 10 has the following functions: the decrease pressure Δp is estimated based on the actual current value Im when the angular acceleration fluctuation is equal to or smaller than the predetermined absolute value excluding the actual current value Im when the angular acceleration fluctuation exceeds the predetermined absolute value.

In addition, the gas spring 8 having a small extension has a small compression ratio of the gas. The gas spring 8 having a small compression ratio reduces the accuracy of estimating the reduced pressure Δp of the gas pressure. In contrast, in the gas spring 8 having a large extension, the decrease pressure Δp can be estimated with high accuracy. From this point of view, it is preferable to obtain the actual current value Im of the drive motor M2 in a state where the absolute value of the angle θc formed by the reference line Lb and the virtual line Lc in fig. 3 is large. From the viewpoint of estimating the reduction pressure Δp with high accuracy, the absolute value of the angle θc is preferably 20 ° or more, more preferably 25 ° or more, and particularly preferably 30 ° or more.

From the standpoint of estimating the reduced pressure Δp with high accuracy, it is preferable to estimate the reduced pressure Δp in the gas spring 8 having a large gas compression ratio. The reduction pressure Δp is preferably estimated in the gas spring 8 with a large bearing torque Tg. The decrease pressure Δp is preferably estimated based on the actual current value Im when the second arm 14 is in a posture that generates a torque Tg of 25% or more of the maximum torque Tgmax borne by the gas spring 8. The decrease pressure Δp is preferably estimated based on an actual current value Im when the torque Tg of 25% or more of the maximum torque Tgmax is generated excluding the torque Tg of less than 25% of the maximum torque Tgmax. The maximum torque Tgmax is the maximum value that can be borne by the gas spring 8 in the robot 2.

Here, the decrease pressure Δp of the gas pressure is estimated, but the decrease state of the gas estimated by the present invention is not limited to this. The gas reduction state may be estimated based on a comparison between the actual current value Im and the theoretical current value Ii of the drive motor M2 in the rotation state of the second arm 14. As the state of gas decrease, the decrease rate Gp of the gas pressure, the gas pressure of the gas spring 8, the gas amount of the gas chamber 30, or the gas leakage amount leaking from the gas chamber 30 may be obtained. Further, as a case of showing the reduced state of the gas, a comparison between the actual current value Im and the theoretical current value Ii of the rotation state of the drive motor M2 may be used as it is.

In the robot 2, the second arm 14 is described as the rotating arm according to the present invention, and the first arm 12 is described as the arm support portion according to the present invention, but the present invention is not limited thereto. For example, a gas spring may be provided between the second arm 14 and the third arm 16, and the second arm 14 may be an arm support portion and the third arm 16 may be a rotation arm. Similarly, a gas spring may be provided between the fourth arm 18 and the fifth arm 20, and the fourth arm 18 may be an arm support portion and the fifth arm 20 may be a rotating arm. The robot 2 according to the present invention will be described by taking a multi-joint robot as an example, but any articulated robot having an arm support portion and a rotating arm may be used.

Fig. 5 is a graph illustrating a change in the air pressure Pa of the air spring 8 when the robot 2 performs a certain operation. The horizontal axis of the graph represents time t(s), and the vertical axis represents pressure P (MPa). The second arm 14 of the robot 2 rotates to expand and contract the gas spring 8. As shown in fig. 5, the air pressure Pa of the air spring 8 increases and decreases according to the rotation of the second arm 14.

Test 1

Fig. 6 (a) shows the difference between the air pressure estimated by the estimation method according to the present invention and the actual air pressure Pa, and the difference between the air pressure estimated by the conventional estimation method and the actual air pressure Pa. In fig. 6 (a), the air pressure of the air spring 8 is estimated in 12 different operations M1 to M12. The diagonal line differential air pressure denoted by reference numeral a is a differential air pressure based on the estimation method according to the present invention. The air pressure difference of the diagonal line denoted by reference symbol B is an air pressure difference based on the existing estimation method. In this conventional estimation method, the reduced pressure Δp of the air pressure is estimated based on the actual current value Im at which the drive motor M2 is in the drive state and the second arm 14 is in the stop state. The difference between the air pressure based on the reduced pressure DeltaP and the actual air pressure Pa is obtained. In fig. 6 (a), the gas pressure of the gas spring 8 in the initial set state is P1 (11 (MPa)). In fig. 6 (a), the pressure P is indicated by a solid line as a reference line, and the pressures pa+1 (MPa) and Pa-1 (MPa) are indicated by a chain line.

As shown in fig. 6 (a), the air pressure difference estimated by the estimation method according to the present invention is smaller than the air pressure difference estimated by the conventional estimation method among 8 kinds of operations of M1, M2, M4, M5, M8, M10, M11, and M12 among 12 kinds of operations. Further, the difference between the air pressure estimated by the estimation method according to the present invention and the air pressure Pa is 1 (MPa) or less in any operation. On the other hand, the difference between the air pressure estimated by the conventional estimation method and the air pressure Pa exceeds 1 (MPa) in the operations M11 and M12. The estimation method according to the present invention can estimate the reduced state of the gas with higher accuracy than the conventional estimation method.

In fig. 6 (b) and 6 (c), the gas pressure difference is obtained in the same manner as in the estimation method of fig. 6 (a), except that the gas pressure of the gas spring 8 in the initial set state is changed. In fig. 6 b, the gas pressure of the gas spring 8 in the initial set state is P2 (9 (MPa)). In fig. 6 (c), the gas pressure of the gas spring 8 in the initial set state is P3 (7 (MPa)). As shown in fig. 6 (b) and 6 (c), even if the air pressure of the air spring 8 is reduced, the estimation method according to the present invention can accurately estimate the reduced state of the air.

[ test 2]

Fig. 7 (a) shows a relationship between the air pressure estimated by the estimation method according to the present invention and the actual air pressure Pa. The air pressure of fig. 7 (a) is estimated based on the actual current value Im when the second arm 14 is in the rotation state. In fig. 7 (a), the horizontal axis represents time t(s), and the vertical axis represents the ratio (P/Pa) of the air pressure P to the actual air pressure Pa. The straight line (Pa/Pa) represents a reference line of the ratio (Pa/Pa) of the actual air pressure Pa to the air pressure Pa. The dots shown by the black dots represent the ratio of the air pressure to the air pressure Pa respectively deduced.

In fig. 7 (a), in the two-dot chain line, the estimated variation in the air pressure is smaller in the areas A1, A2, and A3 than in the other areas. The areas A1, A2, and A3 are each estimated based on an actual current value Im (rotation actual current value Ir) measured in a state where the angular acceleration is constant. The areas A1, A2, and A3 represent the following cases: the deviation is small in the air pressure estimated based on the actual current value Im in a state where the angular acceleration of the drive motor M2 is constant. From the viewpoint of estimating the gas reduction state of the gas spring 8 with high accuracy, the control device 10 preferably has a function of determining the magnitude of the angular acceleration of the drive motor M2. Preferably, the control device 10 has the following functions: the gas reduction state is estimated based on the actual current value Im in a constant state of the angular acceleration excluding the actual current value Im when the angular acceleration of the drive motor M2 fluctuates.

Fig. 7 (b) shows a relationship between the air pressure estimated by another estimation method according to the present invention and the actual air pressure Pa. In fig. 7 b, an actual current value Im (rotation actual current value Ir) when the magnitude of the fluctuation of the angular acceleration of the drive motor M2 is equal to or smaller than a predetermined absolute value is used. Otherwise, the ratio of the estimated air pressure to the air pressure Pa is obtained in the same manner as in the estimation method of fig. 7 (a). The scales on the vertical and horizontal axes of fig. 7 (a) and 7 (b) are the same in size. Fig. 7 (b) shows a smaller deviation of the estimated air pressure than fig. 7 (a). From the viewpoint of estimating the gas reduction state of the gas spring 8 with high accuracy, the control device 10 preferably has a function of determining the magnitude of the fluctuation of the angular acceleration of the drive motor M2. Preferably, the control device 10 has the following functions: the gas reduction state is estimated based on the actual current value Im when the angular acceleration variation of the drive motor M2 exceeds a predetermined absolute value, excluding the actual current value Im when the angular acceleration variation is equal to or less than the predetermined absolute value.

[ test 3]

Fig. 8 shows a relationship between the air pressure estimated by the estimation method according to the present invention and the angle θc (see fig. 3). In fig. 8, the horizontal axis represents the angle θc, and the vertical axis represents the ratio (P/Pa) of the air pressure P to the actual air pressure Pa. The straight line (Pa/Pa) represents a reference line of the ratio (Pa/Pa) of the actual air pressure Pa to the air pressure Pa. The dots indicated by the black dots represent the ratio of the air pressure to the air pressure Pa respectively estimated.

Fig. 8 shows the following case: in the range where the absolute value of the angle θc is large, the deviation of the estimated air pressure is small. The deviation of the estimated air pressure becomes significantly smaller at an absolute value of 20 ° or more of the angle θc. The deviation of the estimated air pressure is further reduced at an absolute value of the angle thetac of 25 deg. or more, and is particularly reduced at an absolute value of the angle thetac of 30 deg. or more.

From the viewpoint of estimating the reduced state of the gas with high accuracy, it is preferable that the control device 10 has a function of determining the absolute value of the angle θc. Preferably, the control device 10 estimates the gas reduction state based on the actual current value Im when the angle θc is equal to or greater than a predetermined angle. The predetermined angle is preferably 20 ° or more, more preferably 25 ° or more, and particularly preferably 30 ° or more.

Fig. 8 shows that the gas spring 8 having a large gas compression ratio estimates the decrease pressure Δp, whereby the decrease state of the gas can be estimated with high accuracy. From this point of view, it is preferable to estimate the reduction pressure Δp in the gas spring 8 having a large bearing torque Tg. The decrease pressure Δp is preferably estimated based on the actual current value Im when the second arm 14 is in a posture that generates a torque Tg of 25% or more of the maximum torque Tgmax borne by the gas spring 8.

Description of the reference numerals

2 … robot; 4 … base station; 6 … robotic arm; 8 … gas spring; 8b … base end portion; 8c … front end; 10 … control means; 12 … first arm (arm support); 14 … second arm (rotating arm); 16 … third arm; 18 … fourth arm; 20 … fifth arm; 22 … sixth arm; 24 … hand; 26 … cylinder; 28 … piston; 30 … gas cell.

Claims

1. A joint robot is provided with:

an arm support part;

a rotating arm rotatably supported by the arm support portion;

a driving motor for rotating the rotating arm;

a gas spring for supporting a load acting on the rotating arm to reduce the load of the drive motor; and

the control device is used for controlling the control device,

the control device has the following functions:

judging the condition that the rotating arm is in a rotating state; and

by determining that the rotating arm is in the rotating state, the actual current value of the driving motor when the rotating arm is in the stopped state is not used, and the gas reduction state of the gas spring is estimated based on the comparison between the actual current value and the theoretical current value of the driving motor when the rotating arm is in the rotating state.

2. The articulated robot of claim 1 wherein,

the control device has a function of determining the magnitude of the fluctuation of the angular acceleration of the drive motor.

3. The articulated robot according to claim 1 or 2, wherein,

the control device uses an actual current value when the rotating arm is in a posture that generates a torque of 25% or more of a maximum torque borne by the gas spring.

4. In a joint robot comprising a rotating arm, a driving motor for rotating the rotating arm, and a gas spring for supporting a load acting on the rotating arm to reduce the load of the driving motor, a gas reduction amount estimating method estimates a gas reduction state of the gas spring,

the gas reduction amount estimation method includes:

an actual current value obtaining step of obtaining an actual current value of the drive motor;

an estimating step of estimating a gas reduction state of the gas spring based on the actual current value,

in the actual current value obtaining step, it is determined that the rotating arm is in a rotating state, and the actual current value of the drive motor when the rotating arm is in a stopped state is obtained without using the actual current value of the drive motor when the rotating arm is in a rotating state,

in the estimating step, a gas reduction state of the gas spring is estimated based on a comparison between the actual current value and the theoretical current value acquired in the actual current value acquiring step.